Advanced analytical techniques requiring small sample sizes and the expense and scarcity of many biologically active materials have created a demand in analytical and research applications for small-scale dialysis equipment and procedures. It is not uncommon that dialysis may be required on fluid samples of less than 500 microliters and frequently less than 150 microliters, such as on the order of 10-100 microliters. Some special problems encountered in dialyzing small samples center on difficulty in handling the sample, loss of sample, and achieving effective dialysis.
Horowitz and Barnes (Analytical Biochemistry, 128,478-480, 1993, entitled "A Simple, Inexpensive, and Precise Microcell For the Exchange Dialysis and Equilibrium Dialysis of Small Samples") describe a device for dialyzing small samples (10-300 microliters). This device is constructed from commonly available 1.5 ml microcentrifuge tubes using a scalpel to cut a ring from the latter. The sample is loaded into the lid of the tube, the dialysis membrane is placed on top, and the ring is closed over the membrane. Preparation and use of the device is time consuming and awkward, sample recovery is difficult, and dialysis is not always achieved due to sample leakage.